A class of silicon containing polymers known as polydimethylsiloxanes is widely employed in the coatings and personal care industries. In coatings formulations, polydimethylsiloxane and its derivatives are being increasingly used for general modification of surface properties as they provide water and oil repellency, stain resistance, barrier properties, surfactant properties and lubricity. In personal care formulations, the use of polydimethylsiloxane and derivatives thereof, particularly dimethicone copolyols, has gained wide acceptance for the latter's surfactant characteristics and positive effect on sensory properties of a given composition.
Attempts to improve the physical properties of such formulations by incorporating dimethicone copolyols into the composition have met with limited success. These polydimethylsiloxane derivatives were frequently incompatible with the polar polymers and/or other ingredients typically contained in coatings and personal care compositions. Often times auxiliary additives have to be employed to compatibilize the polydimethylsiloxane derivative and the anionic and cationic polymers typically used in the coatings and personal care industries to prevent phase separation of the key components during extended storage periods.
Accordingly, efforts have been made to covalently incorporate the polydimethylsiloxane derivatives into the target polymer backbone in an effort to compatibilize the silicone and polymer components of the formulation. U.S. Pat. No. 6,403,074 discloses a silicone containing polymer obtained by polymerizing ethylenically unsaturated monomers in the presence of dimethicone copolyol via a free radical mechanism. The patent disclosure surmises that grafting of the monomers onto the dimethicone copolyol occurs during the polymerization reaction. However, it is not evident from the disclosure to what extent (if any) that the dimethicone copolyol is covalently incorporated into the polymer backbone or whether an interpolymer of the dimethicone copolyol and the free radically polymerized monomers is formed. For polyhydroxy carbinol compounds, chain transfer can often be a significant problem during free radical polymerization, and this may prevent effective copolymerization of such compounds with other ethylenically unsaturated monomers.
In another approach, silicone containing macromers containing terminal unsaturation have been synthesized via the anionic polymerization of hexamethylcylotrisiloxane monomer (D3) to from a living polymer of controlled molecular weight. Termination of the anionic polymerization reaction is achieved via the direct reaction of the living polymeric anion with halogen-containing termination agents, such as, chlorosilane compounds containing a polymerizable vinyl group. The obtained vinyl terminated siloxane containing macromers in turn can be polymerized with other copolymerizable unsaturated monomers to obtain silicone containing copolymers as disclosed in U.S. Pat. Nos. 4,693,935 and 4,728,571. However, the synthesis of these macromers is very difficult and given the relatively high molecular weight of the macromer it is arduous to separate the unreacted impurities from the reaction product.
In U.S. Pat. No. 5,162,472, there is disclosed a vinyl terminated dimethicone copolyol macromer that is prophetically reported to be synthesized by esterifying acrylic acid with a hydroxyl terminated dimethicone copolyol. The reaction mass is heated to 140 to 180° C. and the disclosure states that the purportedly obtained vinyl containing silicone ester is subsequently copolymerized without additional purification. As is well known the esterification of carboxylic acid with an alcohol is a slow reaction with moderate yields for oligomeric or polymeric substrates. Further, is also well known in the art of acrylic acid chemistry that this highly reactive monomer spontaneously dimerizes at room temperatures via a thermally induced ionic mechanism wherein the proton dissociates from the carboxylic acid group forming a carboxylate anion which subsequently adds to acrylic acid via Michael-type addition to give the dimer. This phenomenon is substantially accelerated at increasing temperatures. At the reaction temperatures reported in the '472 disclosure the acrylic acid starting material would rapidly dimerize consuming most if not all of this reactant to yield a complex mixture of products. Given that the esterification of a carboxylic acid with an alcohol is slow and that acrylic acid rapidly oligomerizes at the reaction temperatures reported in the '472 disclosure, it is difficult to perceive how the purported product is obtained. Even if some product is formed it would be difficult, time consuming and costly to separate the desired product from the reaction mass.
A more traditional esterification procedure for functionalizing a dimethicone copolyol with a vinyl end group is to react an acid chloride such as acryloyl chloride with the dimethicone copolyol and employing a base to remove the liberated HCl. The use of the acryloyl chloride eliminates the spontaneous oligomerization issues suffered from the use of acrylic acid as set forth in the '472 disclosure. However, a salt is generated as a by-product of the esterification reaction. Salts are not only difficult to remove from macromers but may also be deleterious to the subsequent polymerization of the macromer.
In addition to the problems faced in synthesizing the foregoing macromers, the polymerization activities of these acrylate-type macromers are similar to the polymerization activities of the comonomers intended for copolymerization into the polymer backbone due to the unhindered nature of the carbon-carbon unsaturation in the terminal vinyl group. It is common practice to vary monomer reactivity as one approach to altering the copolymer structure and thereby the latter's physical and chemical properties.
Accordingly, there is a need for newer silicone containing macromers that are easily synthesized and purified and exhibit polymerization activities that allow flexibility in copolymerization to generate copolymers with desirable properties. We have now unexpectedly discovered such a silicone macromer via a reaction originally intended to prepare readily polymerizable compounds containing the itaconate moiety.
The present invention provides dimethicone copolyol macromers that are easily synthesized and that have unexpected polymerization activities which allow ready copolymerization to generate products with desirable properties. The copolyol macromers of the invention are synthesized from the reaction of a dimethicone copolyol and itaconic anhydride. Dimethicone copolyols contain terminal or pendant polyether groups that terminate in an active hydroxyl group. The reaction of a hydroxy silicone compound such as dimethicone copolyol with a cyclic anhydride is known. As disclosed in U.S. Pat. Nos. 3,560,544 and 5,296,625 the reaction of the active hydroxyl group(s) on the copolyol with the anhydride yields the copolyol half-ester of the anhydride. While these patents disclose the reaction of a dimethicone copolyol with a variety of cyclic anhydrides (including the olefinically unsaturated maleic anhydride), the use of anhydrides containing exocylic olefinic unsaturation is not described or suggested. Moreover, the '544 patent mentions that the derivatized silicone polymer is used as a surfactant, a wetting agent, detergent, emulsifier or fiber lubricant, and the '625 disclosure teaches that the obtained esters are useful in textile and personal care applications to render softness and lubrication to treated substrates. There is no teaching or suggestion in any of these disclosures that the reaction product of a hydroxy silicone with an anhydride containing any type of unsaturation can be employed as polymerizable macromer in the synthesis of polymers and copolymers.
Unexpectedly, it has been discovered that the half-ester formed from the reaction of itaconic anhydride (containing exocylic unsaturation) with a dimethicone copolyol yields a mixture of various isomers of citraconate mono-esters formed from the rapid isomerization itaconic anhydride to citraconic anhydride and subsequent reaction of the citraconic anhydride with the silicone copolyol. More surprisingly, given that the olefinic double bond in the citraconate moiety of the so-formed macromer is sterically encumbered by triple substitution, and the well known fact that trisubstituted olefins do not readily free radically polymerize at useful rates, we have found the citraconate dimethicone copolyol esters are easily copolymerized with a variety of monomers containing free radically polymerizable olefinic unsaturation. This is a novel and unexpected finding in the preparation of ethylenically unsaturated silicone copolyol esters. Itaconic anhydride is known to react with alcohols to generate the expected itaconate esters.